Special Senses Structures and Functions

Ciliary Zonule Function

A halo of fine fibers that extend from the ciliary process around the lens. Functions to attach the lens to the ciliary process.

Nasoclacrimal Duct Function

A single tube that empties into the nasal cavity. Allows lacrimal fluid to flow into the nasal cavity.

Optic Disc Function

Also known as the "blind spot" because it lacks photoreceptors, so light focused on it cannot be seen. The optic disc represents the beginning of the optic nerve and is the point where the axons of retinal ganglion cells come together. The optic disc is also the entry point for the major blood vessels that supply the retina.

Superior Oblique Eye Muscle Function

Depresses eye and turns it laterally. Controlled by the trochlear nerve.

Inferior Rectus Eye Muscle Function

Depresses eye and turns it medially. Controlled by the oculomotor nerve

Inferior Oblique Eye Muscle Function

Elevates eye and turns it laterally. Controlled by the oculomotor nerve.

Superior Rectus Eye Muscle Function

Elevates eye and turns it medially. Controlled by the oculomotor nerve.

Lacrimal Caruncle Function

Fleshy reddish elevation that contains sebaceous and sweat glands. Secretes a whitish oily secretion for lubrication of the eye (can dry and form "eye sand")

Central Fovea Function

In the eye, a tiny pit located in the macula of the retina that provides the clearest vision of all. Only in the fovea are the layers of the retina spread aside to let light fall directly on the cones, the cells that give the sharpest image. Also called the central fovea or fovea centralis.

Lacrimal Apparatus Function

Includes the lacrimal gland and a series of ducts that drain the lacrimal fluid into the nasal cavity. Protects the eye by keeping it moist. Blinking spreads the lacrimal fluid.

Optic Nerve Function

It is the second of several pairs of cranial nerves. The job of the optic nerve is to transfer visual information from the retina to the vision centers of the brain via electrical impulses. The optic nerve is made of ganglionic cells or nerve cells. It consists of over one million nerve fibers.

Ciliary Body Function

Modification of the choroid that encircles the lens. Contains the ciliary muscle and the ciliary process.

Lateral Rectus Eye Muscle Function

Moves eye laterally. Controlled by the abducens nerve.

Medial Rectus Eye Muscle Function

Moves eye medially. Controlled by the oculomotor nerve.

Ciliary Process Function

Radiating folds of the ciliary muscle. Capillaries of the ciliary process form the aqueous humor by filtering plasma.

Conjunctiva Function

Secrete mucus to lubricate the eye. Inflammation of the conjunctiva results in conjunctivitis or "pink eye"

Ciliary Muscle Function

Smooth muscle found within the ciliary body. Alters the shape of the lens with contraction and relaxation.

Cornea Function

Structurally continuous with the sclera; modified to form a transparent layer that bulges anteriorly. Functions to forms a clear window that is the major light bending (refracting) medium of the eye.

Iris Function

The anterior function of the vascular layer that is pigmented. It contains two layers of smooth muscle (sphincter pupillae and dilator pupillae). Functions to allow light to enter the eye.

Retina Bipolar Cell Layer Function

The bipolar cells process input from photoreceptors and horizontal cells, and transmit the signal to their axons.

Medial and Lateral Commissures Function

The commissures are the junctions where the eyelids meet medially and laterally. Form the corners of the eyes. The medial commissure contains the lacrimal caruncle.

Conjunctiva Description

The conjunctiva is a transparent mucous membrane. It lines the eyelids as the palpebral conjunctival and folds back over the anterior surface of the eyeball as the balbar conjunctiva. The bulbar conjunctiva covers the white of the eye, not the cornea. The bulbar conjunctiva is very thin, and blood vessels are clearly visible beneath it.

Retina Description

The innermost layer of the eyeball is the delicate retina, which develops from an extension of the brain. It contains (1) millions of photoreceptors that transduce (convert) light energy; (2) other neurons involved in processing responses to light; (3) and glia.

Lacrimal Canaliculi Function

The lacrimal canaliculi are two tiny canals that are located in the eyelids. They allow for lacrimal fluid to drain into the lacrimal sac.

Lacrimal Gland Function

The lacrimal gland is located in the superior and lateral aspects of the orbit of the eye. The lacrimal gland secretes lacrimal fluid, which contains mucus, antibodies, and lysozyme.

Lacrimal Sac Function

The lacrimal sac is a single pouch located in the medial orbital wall. It allows for lacrimal fluid to drain into the nasolacrimal duct.

Lens Function

The lens is a biconvex, transparent, flexible structure that can change shape to precisely focus light on the retina.

Pupil Function

The pupil is the round central opening of the iris that functions to allow light to enter the eye.

Retina Function

The purpose of the retina is to receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition

Retina Ganglion Cell Layer Function

There are about 0.7 to 1.5 million retinal ganglion cells in the human retina.[2] With about 4.6 million cone cells and 92 million rod cells, or 96.6 million photoreceptors per retina,[3] on average each retinal ganglion cell receives inputs from about 100 rods and cones.

Lacrimal Puncta

Two tiny openings on the medial margin of each eyelid. Allows lacrimal fluid to drain into the superior and inferiorly located lacrimal canaliculi.